Captive shoulder nut having spring tie-down

ABSTRACT

A captive shoulder nut for a electronic module heat sink has a threaded nut portion and a tubular portion extending therefrom. A ramped section in the exterior wall of the tubular portion leads to a retaining groove adjacent the bottom face of the nut portion. A compression spring is slipped over the tubular portion to ride over the ramped section and be retained at one end in the retaining groove. The tubular portion is suitable to be inserted through a straight hole, whereof the inner diameter of the spring is larger than the hole. The free end of the tubular portion is suitable to be flared to a larger diameter than the hole, thereby establishing a captivation.

BACKGROUND OF THE INVENTION

In assembling electronic components and modules, inserts, spacers and standoffs have been often used. The attachment of components and parts has been accomplained by screws spring clips, clamps and other such devices. In a chassis for holding electronic components, space for the manual manipulation of parts and tools often is an issue.

Captives screws and captive fasteners are devices used to fasten two components together, where the fastener remains with one of the components when loosened. Typically a captive screw is “caught38 by component it remain with by a flange, a ferrule, a spring clip or the like, which structure prevents the total removal of the captive fastener from that component The usefulness of captive fasteners is that they do not get lost or fall out of the associated component before and during assembly.

This feature has become very useful in the assembly and removal of components associated from electronic module boards, peripheral component interconnect boards (PCI boards), and printed circuit boards (PC boards), and in the environment of the chassis for housing these boards.

Modern large scale integrated (LSI) circuits, microprocessors, microchips and other integrated circuit devices (IC chips) generate a substantial amount of heat, especially when operating at very high frequencies. Such heat generation can amount to 10's of watts and even 100'of watts of heat per hour. It has become imperative to mount heat sinks on these IC chips to dissipate as much heat as possible. In such instances the heat sink is mounted to the board or to a mounting frame which in turn is mounted to the board which the IC chip is also mounted.

Spring clips have been used to hold heat sinks to IC chips on PC boards. However, these clips are sensitive to vibration, often interfere with the heat transfer fins on the heat sink and are often hard to positively snap into place and to release.

Captive screws have provided and improvement over heat sink clips. Two or four captive screws are used and engage respective flanged corners of the a heat sink. These captive screws have threaded ends which usually engage a threaded ferrule or threaded bushing mounted into a hole through the PC board. They also required a ferrule or bushing though the heat sink's flange through which they extend.

A captive screw may use a slip ring, annular flange, or projecting shoulder positioned on the captive screw at a location below the heat sink flange's surface. This projecting structure prohibits the captive screw from being withdrawn out of the heat sink and thereby holds the fastener captive on the heat sink. Captive screws are generally driven (tightened and loosened) by tool engagement with their head. Typically, captive screws have Phillips, slotted, or TORX heads requiring appropriate screw drivers.

Oftentimes a sheet of compressible elastomeric heat transfer polymeric material is used between the top surface of the IC chip and the bottom of the heat sink. This heat transfer interface material takes up for any surface irregulanties in the mating IC chip and heat sink.

Captive screws for IC chip heat sinks with heat transfer polymeric sheeting have incorporated spring tie-down designs where the tie-down force exerted by the captive screw is governed by the spring force of a compresses spring. This structure permits the heat sink to “float”,i.e., move through expansion and contraction as the IC chip temperature changes.

As the chassis for electronic modules is made smaller with a smaller foot print, and as more boards are crowned into tightly spaced racks in a chassis, the size and position of heat sink tie-down screws, including captive screws, becomes an issue. Moreover, Phillips, slotted and even TORX heads can round out with poor tool alignment. The use and installation of

DISCUSSION OF THE PRIOR ART

The Examiner has cited two anticipation references. To be an anticipation reference, that reference must show every element claimed and must teach the same interconnection and assemblage of those elements. The Examiner's first anticipation reference is DiRago (U.S. Pat. No. 3,816,010) and the second anticipation reference is Fratterola et al (U.S. Pat. No. 5,611,654). Applicant does not believe that each anticipation reference teaches and shows each of the elements opined by the Examiner and therefore the standing 35 USC 102(b) rejection of claims 1-4 and 15; and the standing 35 USC 102(b) rejection of claims 1-11, 13, and 15-17 is respectfully traversed.

DiRago shows a captive nut 22b having a tubular sleeve 22 portion extending there from to terminate in a free end 22b. The tubular sleeve 22 extends through a hole in the arm (plate) 12. A second plate 14 has a pin with a retaining head 20a, with the shaft of the pin 20 extending through the plate 14. The lead end (free end of the pin 20 carries an external thread 20b for engaging the internal thread 24 of the nut 22b. A spring 26 which seats against the outside face of the plate 12 and the shoulder 28 on the nut, biases the nut 22a and its tubular sleeve 22 outwardly from the plate 12. The free end of the sleeve is “rolled over” inwardly to be compressed about the shaft of the pin. As the end 22b of the sleeve 22 is crimped to a smaller dimension than the threaded portion 20b of the pin 20, the nut 22a is captivated to the pin 20 holding the assembly from coming apart. See FIG. 3 and col. 2, lines 25-53.

Frattarola shows a captive nut 10 having an internal threaded knob 20. The nut 10 is held captive to cylindrical hollow ferrule (sleeve) 30, which itself is anchored into a plate 80. The nut 10/20 is fee to move on the sleeve 30. While Frattarola shows a series of ways to anchor his ferrule/sleeve 30 to his plate, the sleeve 30 is always a separate and distinct member from the threaded nut (knob 20). The knob 20 is captivated to the ferrule 30 because the annular flange 37 on the ferrule 30 extends outwardly to engage the captivation means 50, which is actually an inward projecting annular lip or flange 21. See col. 4, lines 13-23. Frattarola does not teach a tubular sleeve extending from his nut 20; nor does he teach a nut with a tubular sleeve extending there from; nor does he teach a sleeve member attached to a nut member and extending from one face thereof. The Frattarola nut 20 is not connected to his retaining ferrule 30.

The Examiner has recited obvious rejections under 35 USC 103(a) opining on several obviousness combinations of prior art. These are each traversed.

To establish a prima facie case of obviousness the following three basic criteria must be met: 1) there must be some suggestion or motivation, either in the references themselves or in the knowledge generally available to one of ordinary skill in the art to combine the specific reference(s) teachings; 2) there must be a reasonable expectation of success in combining the specific reference(s) teachings; and 3) the prior reference (or references when combined) must teach or suggest all of the claim limitations. See MPEP 706.02. The teachings or suggestion to combine and the reasonable expectation of success must both be found in the prior art and not based upon the applicant's disclosure. In re Vaeck, 947 F.2d 488, 20 USPQ2d 1438 (Fed Cir 1991); also see MPEP 2143-2143.03 for additional decisions pertinent to each of the criteria. The initial burden is on the Examiner to provide support for a prima facie case. Ex parte Clapp, 277 USPQ 972, 973 (Bd. Pat. App. & Inter. 1985).

The Examiner has provided no explanation on how the teachings of Kirish (U.S. Pat. No. 4,204,566), Garuti (U.S. Pat. No. 5,042,880) or Witchger (U.S. Pat. No. 2151255) can be combined readily with DiRago, or why there would be a motivation to do so.

Kirrish does not show a sleeve, but a threaded bolt with a pan head and a external annular groove between the pan head and the treads, whereby this groove holds a spring. No hollow sleeve is shown nor suggested by Kirrish. As Kirrish shows a solid bolt and not a hollow sleeve, there is not a wall shown by Kirrish, and there is not a ramped section in any exterior wall, shown by Kirrish. A bolt has no wall as it is a solid shaft-like structure.

Garuti shows a lug nut 68 with self-centering conical lead edge 97 (i.e., flange), which lead flange is typical of automotive lug nuts. He cuts an annular groove 84 in the conical lead flange 97 to captivate the end coil of a spring 70. The other end of the spring 70 is attached to the wheel with an anchor screw 78. The nut 68 bottom thread 97 extends below the groove 84. See FIGS. 3 and 4 and col. 5, lines 11-42. Garuti neither shows nor suggests a sleeve. His entire structure is a solid lug nut with an internal thread. The lug nut is normally attached (screwed onto) a vehicle wheel stud 60. The spring 70 which is attached to the wheel also captivates the lug nut. What Garuti teaches is a quick change wheel carrying its own lug nuts, which are attached to the wheel with springs. In that manner, a pit crew mechanic will not loose the lug nuts when changing race wheels.

Witchger shows a four piece spring nut, having an internal threaded knob/nut (FIG. 2), a T-shaped washer (FIG. 3) a spring (FIG. 4) which mounts between an annular groove 4 in the threaded nut and an annular groove 8 in the washer. However, the grooves 4 and 8 have no tapered lead-in. The spring has pointed ends 10 at either end thereof to screw onto the respective grooves 4 and 8. The assembly is mounted onto a plate 13 (FIG. 1) with a bolt having an enlarged flange 14 and a threaded shaft 11. Witchger neither suggests nor shows a captivation of the nut to the plate nor the bolt to the plate. What is captivated is the washer being held to the nut with the spring. Therefore, a mechanic does not have to fumble with the nut and washer when screwing the nut onto the threaded 11 bolt 12 extending through the plate 13. Witchger does not show a hollow sleeve member attached to and extending from his nut. The nut body is threaded its entire depth. The nut merely has a knurled head portion which lends to finger tightening.

Further the Examiner has provided no explanation on how the teachings of Kirish (U.S. Pat. No. 4,204,566), and Currier (U.S. Pat. No. 3,209,806) can be combined readily with DiRago, or why there would be a motivation to do so.

While Currier does show a threaded 14 thumbscrew which passes through a bushing 40, whereof the bushing 40 has a flange-shaped head 41 for seating into a plate. The bushing end opposite the flanged head 41 has an undercut or counterbored portion 45. The head 11 of the thumbcrew has a conical recess 13 about the attachment of the shank 12 with the head. An annular collar 15 is positioned on the shank 12 at a point between the head and threads 14 of the thumbscrew fastener. Surrounding the bushing 40 is a standoff sleeve 20. When the fastener is screwed onto an object not shown by the reference, the head 11 is driven towards the bushing 40 and the sloped conical surface crimps the end of the undercut bore 45 end 49 inward. See FIG. 3. As the thumbscrew completes its travel, the counterbored portion 45 is completely crimped against the shank 12 and then expands outwardly to catch the counterbored portion 24 of the standoff 20. See FIG. 4. This clamps the standoff 20 to the bushing 40 which in turn is clamped to the plate 30. The thumbscrew 10 is free to slide slightly into and out of the bushing, until the collar 15 stops its outward movement as the outside diameter of the collar is larger than the crimped in opening in the end 49 of the bushing. Thus the bushing 40 captivates the thumbscrew 10. However, there is no bushing suggested by Currier that extends from a nut. Nor is the end of the bushing 40 flared, i.e., “flared out”. To the contrary, Currier teaches crimping inward the end 49 of his bushing 40 to captivate the collar 15, just as DiRago crimps inward his end 22b.

In a further combination of DiRago, Fratterola and Kirrish, the Examiner opines that Fratterola shows a tubular sleeve 30 which is flared out. As discussed above, Fratterola expressly recites a flange 37 on his ferrule 30 and neither recites nor suggests that the flange 37 is a flared end. A flare is made by expanding outwardly. A flange is made by machining, stamping or swaging. Moreover, as previously discussed, the Fratterola ferrule 30 is a separate member, independently secured to the plate 80, and captivating the nut 10 by engaging the nut inward lip 21, whereof the nut is free to slide on the ferrule 30.

In a further combination of Paul (U.S. Pat. No. 5,845,673) and Fratterola, the Examiner opines that Paul flares outwardly the free end of his tubular sleeve at 9b and 22 in FIGS. 6 and 7. Paul expressly recites that portion 22 is a flange, not a flare, whereof Paul further expressly recites that the outer end of the neck 9B is waged onto the flange portion 22 to secure the nut 9. See col. 3, lines 45-50.

The Examiner is put on notice that a flange at the end of a cylinder does not define a “flared end”. Every plumber (and many not plumbers) know(s) how to flare the end of copper, brass or aluminum tubing with a flaring tool.

Wester's New College Dictionary defines “flare” as: means to expand outward in shape as a skirt. It defines “swage” as: to bend or shape with a hammer. These dictionary definitions agree with the use of these terms in the prior art and with applicant's use in the present application. 

1. A captive shoulder nut assembly, comprising: a threaded nut; a tubular sleeve connected to and extending from said threaded nut; and a spring mounted on said tubular sleeve and secured thereto at a location inboard from the free end of said tubular sleeve, said free end being located at an end of the tubular sleeve opposite the threaded nut; wherein said free end has a counter sunk section extending thereinto suitable for flaring.
 2. The captive shoulder nut assembly of claim 1, wherein said spring securement location to said sleeve is adjacent said threaded nut.
 3. The captive shoulder nut assembly of claim 2, wherein said tubular sleeve includes a ramped section in its external wall adjacent said spring securement location and way from said threaded nut.
 4. The captive shoulder nut assembly of claim 3, wherein said ramped section of said sleeve external wall increases outwardly as it approaches said securement location and wherein said securement location of said sleeve includes a retaining groove between said ramped section and said threaded nut end thereof.
 5. (canceled)
 6. The captive shoulder nut assembly of claim 4, wherein said spring is retained by said retaining groove.
 7. The captive shoulder nut assembly of claim 6, wherein said tubular sleeve also includes an undercut section of its interior wall leading from its free end to form said counter sunk bore section.
 8. The captive shoulder nut assembly of claim 7, wherein said tubular sleeve has its counter sunk bore section free end flared outwardly.
 9. (canceled)
 10. The captive shoulder nut assembly of claim 7, wherein said tubular sleeve also includes an annular groove in its exterior wall inboard and adjacent the counter sunk bore section free end.
 11. The captive shoulder nut assembly of claim 10, wherein said tubular sleeve has its free end flared outwardly from the location of said exterior annular groove.
 12. The captive shoulder nut assembly of 8 wherein said threaded nut and said tubular sleeve are of one continuous material.
 13. The captive shoulder nut assembly of claim 8, wherein said threaded nut and said tubular sleeve are of two dissimilar materials, said tubular sleeve being secured to said threaded nut.
 14. A method of assembling a captive shoulder nut assembly through a straight hole in a plate, comprising the steps of; providing a nut with a tubular sleeve connected to and extending therefrom; mounting a compression spring externally around the tubular sleeve; securing an end of the compression spring on the tubular sleeve adjacent where the nut which meets the tubular sleeve; passing the sleeve through said hole in the plate, which hole has a diameter which is smaller than the inside diameter of the compression spring; depressing the spring so that the free end of the tubular sleeve extends beyond the hole; and flaring outwardly the free end of the sleeve to a diameter larger than the hole to captivate the nut and tubular sleeve to the plate.
 15. A captive nut assembly, comprising: a nut member, having an interior opening; a sleeve member, attached to said nut member and extending from one face thereof in alignment with the interior opening thereof and terminating in a fee end; and a spring member mounted outside the exterior wall of said sleeve member and secured at a location inboard of the free end of said sleeve member; wherein the free end of the sleeve member is suitable for flaring.
 16. The captive nut assembly of claim 15, also including a retaining groove in the exterior of the wall of said sleeve member and adjacent said one face of said nut wherein an end of said spring member is retained in said retaining groove.
 17. The captive nut assembly of claim 16, wherein said free end of said sleeve member has its interior undercut into a counter sunk bore, said counter sunk bore portion of said sleeve member being said end suitable for flaring.
 18. The captive nut assembly of claim 17, in combination with a plate, wherein said plate has a straight through hole, wherein said sleeve member extends through said hole, wherein said hole is of a smaller opening than the size of said spring member, thereby restraining said spring member from passing therethrough.
 19. The captive nut assembly of claim 18, wherein said sleeve member carries a V-shaped groove in the exterior of the wall thereof, said V-shaped groove been adjacent said counter sunk bore, and wherein the free end of said sleeve member is formed by being flared outward from the proximate location of said V-shaped groove to extend to a larger diameter than the diameter of said through hole thereby captivating said sleeve member within said hole.
 20. The captive nut assembly of claim 19, wherein said captivating of said sleeve member also captivates said connected nut member and said spring member. 